In the gas turbine, compressed air from a compressor is fed into a combustor, and high temperature gas generated by combusting fuel with the compressed air is fed into a turbine portion, thus driving the turbine portion. Vanes and blades are provided alternatingly along the rotational axis of the turbine portion in a plurality of stages. Some of the compressed air is extracted and the extracted compressed air is fed into the vanes and blades of the turbine portion as cooling air.
To further describe the cooling of the blades, a plurality of disk holes are formed in a rotor disk, to which the blades are attached, at intervals on a circumference of the rotor disk about the rotational axis (at equal angle intervals, for example; however, there are cases in which they are not at equal angle intervals). The extracted air that has been cooled by passing through a cooler is used as the cooling air (or the extracted air is used as the cooling air as it is, without using the cooler). The cooling air is caused to pass through the disk holes, thus supplying the cooling air to each of the rotor disks provided in the plurality of stages along the rotational axis. The cooling air supplied to the rotor disks is fed into the interior of the blades through flow channels inside the rotor disks, and cools the blades from the inside.
As technology to cool the blades, a technology is proposed that supplies the cooling air to the disk holes of the rotor via a so-called Tangential On Board Injection (TOBI) nozzle (see Japanese Patent No. 4146257B). The TOBI nozzle is to supply the cooling air to the disk holes as a circulating flow along the rotational direction of the rotor, and as a result, pumping loss can be reduced.
Specifically, if the cooling air that does not have a flow velocity component in the rotational direction of the disk is supplied to the disk holes, when the cooling air flows into the interior of the disk, energy loss (pumping loss) occurs, leading to reduced performance of the gas turbine. Here, by imparting the flow velocity component in the rotational direction of the rotor to the cooling air and thus generating the circulating flow, a difference between the flow velocity component in the rotational direction of the cooling air and a rotational speed of the rotor is made small, and the occurrence of pumping loss is suppressed.
However, in the above-described technology, some of the compressed air supplied as combustion air to the combustor is extracted, and the extracted compressed air is used as the cooling air. Therefore, the amount of the compressed air supplied to the combustor and a combustion amount of the combustor is reduced by an amount corresponding to the air extracted as the cooling air, and the turbine output thus deteriorates. Further, when the extracted air is passed through the cooler and cooled before being used as the cooling air, power to perform the cooling by the cooler is required, and this results in energy loss.
When the TOBI nozzle is used, pumping loss can be suppressed and the turbine output can be improved. However, it is desirable to further improve the turbine output.